1. Field of the Invention
The present invention relates to a fixing member for use in a heat-fixing apparatus in an electrophotographic image forming apparatus such as a copier and a laser beam printer, and a fixing apparatus having the fixing member.
2. Description of the Related Art
In general, in a heat-fixing apparatus for use in an electrophotographic system, rotation members such as a pair of a heated roller and a roller, a film and a roller, and a belt and a roller are in pressure-contact with each other. When a material to be recorded, holding an image formed by an unfixed toner, is introduced to a pressure-contact portion formed between the rotation members, the unfixed toner on the material to be recorded is heated and molten to allow the image to be fixed on the material to be recorded. The rotation member with which the toner held on the material to be recorded is contact is referred to as a fixing member, and is called a fixing roller, a fixing film or a fixing belt depending on the form thereof.
As such a fixing member, a member is known in which a cured silicone rubber layer having heat resistance is disposed on a substrate made of a metal, a heat-resistant resin or the like, and covered with a fluorine resin with an addition curing type silicone rubber adhesive interposed therebetween. For formation of the cured silicone rubber layer, an addition curing type silicone rubber composition is often used from the viewpoint of processability.
The cured silicone rubber layer formed using the addition curing type silicone rubber composition has a crosslinking structure having a carbon-carbon bond built up by an addition reaction of an unsaturated aliphatic group in the addition curing type silicone rubber composition with an active hydrogen group bound to silicon (Si—H group) by heating. The cured silicone rubber layer has such a crosslinking structure to thereby exhibit excellent elasticity. The fixing member having the above configuration can enclose and melt a toner image, without excessively compressing and collapsing the toner image, by means of excellent elasticity of the cured silicone rubber layer. Therefore, the fixing member has an effect of preventing image displacement and bleeding to improve color mixing properties.
When the fixing member having the cured silicone rubber layer formed using the addition curing type silicone rubber composition is heated by a heat source such as a heater in a fixing process over a long period, however, the carbon-carbon bond in the crosslinking structure in the cured silicone rubber layer may be cleaved to deteriorate elasticity of the cured silicone rubber layer over time. Such a phenomenon is known as the aging phenomenon of a cured silicone rubber.
In the fixing member having the cured silicone rubber layer, the degree of elastic deformation may be thus changed over time in use, thereby resulting in the change in quality of an electrophotographic image over time. The fixing member has the important problem of having a suppressed change in elasticity of the cured silicone rubber layer, in order to ensure a stable image quality.
Against such a problem, Japanese Patent No. 4597245 discloses that it is effective to allow an unsaturated aliphatic group to be present in a cured silicone rubber layer. The reason for this is because, even if a carbon-carbon bond in the cured silicone rubber layer is cleaved, the unsaturated aliphatic group is present in the cured silicone rubber layer to thereby be subjected to a radical addition reaction, thereby building up a crosslinking structure again to suppress the deterioration in elasticity of the cured silicone rubber layer.
A fixing member disclosed in Japanese Patent No. 4597245 has a configuration in which an addition curing type silicone rubber adhesive is used to bond a fluorine resin layer onto the cured silicone rubber layer. Then, the surface of the cured silicone rubber layer in the fixing member is irradiated with ultraviolet ray in the production process of the fixing member. Thus, the surface of the cured silicone rubber layer can have an enhanced degree of crosslinking, and a dense structure can be formed. Therefore, an addition curing type silicone rubber adhesive having an active hydrogen group, with which the surface of the cured silicone rubber layer is to be coated, can be inhibited from being penetrated into the cured silicone rubber layer. As a result, the reaction of the unsaturated aliphatic group in the cured silicone rubber layer with the active hydrogen group in the addition curing type silicone rubber adhesive can be suppressed, and the unsaturated aliphatic group can be present in the cured silicone rubber layer in a large number.